SRAM Spectro S7 hub spectacularly killed

[Chalo]

Hi y'all,

I was riding around town yesterday on my 29er equipped with a SRAM
Spectro S7 gearhub and 40/21 primary gearing. As I came to a short,
steep uphill section of gravel alley, I downshifted to first gear and
turned up my effort to climb the rise without having to get off and
push.

My hub said "pop!" and my pedals sagged out from underneath me. A
quick triage operation established that instead of the usual
[1-2-3-4-5-6-7] shift sequence, I was instead getting [N-N-
N-4-4-4-4]. After the "event", there was no unusual noise, crunching,
or balkiness in the hub-- just smooth freewheeling in both directions
for gears 1-3 and normal 1:1 single-speed drive in gears 4-7.

I hope to take apart the hub and do a postmortem soon. But until
then, does anybody have a guess what let go inside, and whether it's a
reasonably fixable issue?

Chalo

 

[Leland Mayne]

Chalo wrote:
> Hi y'all,
>
> I was riding around town yesterday on my 29er equipped with a SRAM
> Spectro S7 gearhub and 40/21 primary gearing. As I came to a short,
> steep uphill section of gravel alley, I downshifted to first gear and
> turned up my effort to climb the rise without having to get off and
> push.
>
> My hub said "pop!" and my pedals sagged out from underneath me. A
> quick triage operation established that instead of the usual
> [1-2-3-4-5-6-7] shift sequence, I was instead getting [N-N-
> N-4-4-4-4]. After the "event", there was no unusual noise, crunching,
> or balkiness in the hub-- just smooth freewheeling in both directions
> for gears 1-3 and normal 1:1 single-speed drive in gears 4-7.
>
> I hope to take apart the hub and do a postmortem soon. But until
> then, does anybody have a guess what let go inside, and whether it's a
> reasonably fixable issue?
>
> Chalo

It depends on what happened. If it's just one of the springs getting
tangled or a ball cage coming apart & jamming it can probably be fixed.
If any other piece of metal broke it's dead. Internal parts are not
available in North America. There are fairly good diagrams available on
the SRAM web site to help getting it all back together but you have to
poke around a bit to find them. On the newer models you need an extra
large (22mm?) cone wrench. Be careful of the phases of the planet gears
when you put it back together, there's a spot on the top that needs to
be in the same orentation for all 3 gears.

Leland

 

[landotter]

On Apr 25, 12:51 pm, Chalo <[email protected]> wrote:
> Hi y'all,
>
> I was riding around town yesterday on my 29er equipped with a SRAM
> Spectro S7 gearhub and 40/21 primary gearing. As I came to a short,
> steep uphill section of gravel alley, I downshifted to first gear and
> turned up my effort to climb the rise without having to get off and
> push.
>
> My hub said "pop!" and my pedals sagged out from underneath me. A
> quick triage operation established that instead of the usual
> [1-2-3-4-5-6-7] shift sequence, I was instead getting [N-N-
> N-4-4-4-4]. After the "event", there was no unusual noise, crunching,
> or balkiness in the hub-- just smooth freewheeling in both directions
> for gears 1-3 and normal 1:1 single-speed drive in gears 4-7.

I demand my money back, that was not spectacular. I wanted a
description like a cartoon with loose wheels and random squirrels
flying through a fog of bearings. Stinks though. Hope Leland's right--
could just be a simple spring. Good excuse to mess with it at any rate.

 

[Chalo]

landotter wrote:
>
> Chalo wrote:
> >
> > My hub said "pop!" and my pedals sagged out from underneath me. A
> > quick triage operation established that instead of the usual
> > [1-2-3-4-5-6-7] shift sequence, I was instead getting [N-N-
> > N-4-4-4-4]. After the "event", there was no unusual noise, crunching,
> > or balkiness in the hub-- just smooth freewheeling in both directions
> > for gears 1-3 and normal 1:1 single-speed drive in gears 4-7.
>
> I demand my money back, that was not spectacular. I wanted a
> description like a cartoon with loose wheels and random squirrels
> flying through a fog of bearings.

Fair enough. I could at least have had the decency to dive face-first
off the bike for another round of haphazard DIY cosmetic surgery
(complete with photos!!)

I think of it as spectacular, though a better term might be
"catastrophic", whenever a bike part dies with a bang instead of a
whimper.

> Stinks though. Hope Leland's right-- could just be a simple spring.
> Good excuse to mess with it at any rate.

It will be a good excuse to tear into it, and a good excuse to try out
a new Alfine hub if that should prove necessary. (Complete with rear
disc brake, natch.) If the money fairy smiles on me, it might even
become "necessary" to "experiment" with another Rohloff hub.

This bike is the temporarily de-electrified version of my 'lectric
bike. If I can't fix it up to my complete satisfaction, then it will
also be a good excuse to build yet another power-assist machine, stout
as Vulcan's anvil. So it's all for the good, in its way. I'm sure my
wife will come around to my way of thinking on this.

Chalo

 

[jim beam]

Chalo wrote:
> Hi y'all,
>
> I was riding around town yesterday on my 29er equipped with a SRAM
> Spectro S7 gearhub and 40/21 primary gearing. As I came to a short,
> steep uphill section of gravel alley, I downshifted to first gear and
> turned up my effort to climb the rise without having to get off and
> push.
>
> My hub said "pop!" and my pedals sagged out from underneath me. A
> quick triage operation established that instead of the usual
> [1-2-3-4-5-6-7] shift sequence, I was instead getting [N-N-
> N-4-4-4-4]. After the "event", there was no unusual noise, crunching,
> or balkiness in the hub-- just smooth freewheeling in both directions
> for gears 1-3 and normal 1:1 single-speed drive in gears 4-7.
>
> I hope to take apart the hub and do a postmortem soon. But until
> then, does anybody have a guess what let go inside, and whether it's a
> reasonably fixable issue?
>
> Chalo

all these hubs have torque specs, which you can easily exceed. this
should therefore not really be at all surprising.

 

[Chalo]

jim beam wrote:
>
> Chalo wrote:
>
> > I hope to take apart the hub and do a postmortem soon. But until
> > then, does anybody have a guess what let go inside, and whether it's a
> > reasonably fixable issue?
>
> all these hubs have torque specs, which you can easily exceed. this
> should therefore not really be at all surprising.

I've been riding on various gearhubs for about ten years. This is the
first one I've busted up internally (though certainly not the first
one I've had some trouble with).

If a bike part has a capacity rating, I generally exceed it. I'm used
to that. I try to stick with stuff whose real capacity is known to
exceed its rating, or whose useful lifespan and failure
characteristics are otherwise acceptable.

A couple of weeks ago, I wasted an 8/9 speed cassette body, while
using a modest 36t ring. In that case, my pedals didn't fall away--
rather the thing crunched and then stopped freewheeling. I suppose I
could limit myself to trials-proven single freewheels or (worse yet)
fixed gearing, but where's the fun in that?

Chalo

 

[Dan Burkhart]

Hi y'all,

I was riding around town yesterday on my 29er equipped with a SRAM
Spectro S7 gearhub and 40/21 primary gearing. As I came to a short,
steep uphill section of gravel alley, I downshifted to first gear and
turned up my effort to climb the rise without having to get off and
push.

My hub said "pop!" and my pedals sagged out from underneath me. A
quick triage operation established that instead of the usual
[1-2-3-4-5-6-7] shift sequence, I was instead getting [N-N-
N-4-4-4-4]. After the "event", there was no unusual noise, crunching,
or balkiness in the hub-- just smooth freewheeling in both directions
for gears 1-3 and normal 1:1 single-speed drive in gears 4-7.

I hope to take apart the hub and do a postmortem soon. But until
then, does anybody have a guess what let go inside, and whether it's a
reasonably fixable issue?

Chalo

OK,I'll bite. Here's my guess. I'm betting the spring that allows the ring gear to move toward the drive side to engage the hub pawls in the high gears was already weak. Then you were putting massive torque to the pedals in first gear when the only feeble interface in an otherwise robust hub failed. That would be the teeny weeny clutch teeth that engage the coupler gear to the ring gear in gears 1 through 3.
This failure would not be related to the weak spring, but the spring is the only way I could explain direct drive in your top 4.
If the ring gear pawls fail to engage the hub when you shift to gears 5 to 7, the planet carrier pawls will drive the hub. With the clutch engaged to the planetary carrier, you have direct drive.
Dan Burkhart
www.boomerbicycle.ca

 

[(PeteCresswell)]

Per Chalo:
>If a bike part has a capacity rating, I generally exceed it. I'm used
>to that.

Have you managed to toast a Rohloff hub yet?
--
PeteCresswell

 

[Chalo]

PeteCresswell wrote:
>
> Per Chalo:
>
> >If a bike part has a capacity rating, I generally exceed it. I'm used
> >to that.
>
> Have you managed to toast a Rohloff hub yet?

Nope. I've had no mechanical problems at all with my Rohloff hub. The
only repair I have had to make has been to replace the rubber cuff on
the shifter when it unstuck and worked loose.

The Rohloff Speedhub is specifically approved for tandem use. It has
a specified minimum gearing ratio of 38/16 for single bikes and 40/16
for tandems. I put 44/16 on mine just to be on the safe side. I'm
not only heavy without being debilitated, but I use 205mm cranks on
that bike, which effectively lowers the ratio of the primary
gearing.

Chalo